The present invention relates to a crystal oscillator, and more particularly, to a self-powered crystal oscillator and a method thereof that utilizes a power injection technique to compensate energy loss of crystal unit and consume low power.
Real-time keeping is a widely demanded function by various electronic devices, such as digital camera, GPS navigation system, mobile phone, and etc. A 32.768 kHz crystal (XTAL) with oscillation circuit is typically adopted for the generation of the real-time clock due to its high frequency stability against environmental variations. On the other hand, some of the electronic devices are portable and equipped with batteries having limited capacity. To maximize battery life, developers must minimize power consumption of components including the crystal oscillators of the electronic devices.
In the related art, the Pierce oscillation circuit is a widely-used architecture for a crystal oscillator. The Pierce oscillation circuit has sub-uW power consumption that is achievable through amplitude control technique disclosed by W. Thommen in ““An Improved Low Power Crystal Oscillator”, Proc. of the 25th ESSCIRC, pp. 746-749, September, 1999”. To reduce extra power consumption induced by the large load capacitor required by the Pierce oscillator, a differential oscillator is disclosed by D. Ruffieux in ““A High-Stability, Ultra-Low-Power Quartz Differential Oscillator Circuit for Demanding Radio Applications,” Proc. Of the 28th ESSCIRC, pp. 85-88, September, 2002”. However, both of disclosed architectures require amplifiers that are operated in the linear region and consume considerable static power, which imposed a great difficulty to reduce the power consumption of the crystal oscillator